Key takeaways
- Suji comes from the geometry of two-sided suited blocks; no tile is inherently safe.
- The six basic relationships are 1–4, 2–5, 3–6, 4–7, 5–8, and 6–9.
- Suji removes selected two-sided routes but not inside, edge, double-pair, or single waits.
- Every inference belongs to one opponent; discard rows from different players cannot be combined.
- Riichi furiten gives the inference stronger rules support. Without it, suji remains only a relative clue.
Where does suji come from?
A two-sided block waits on two numbers three apart:
| Block | Wait | Suji |
|---|---|---|
| 23 | 1, 4 | 1–4 |
| 34 | 2, 5 | 2–5 |
| 45 | 3, 6 | 3–6 |
| 56 | 4, 7 | 4–7 |
| 67 | 5, 8 | 5–8 |
| 78 | 6, 9 | 6–9 |
Seeing 4m therefore draws attention to 1m and 7m. Seeing 5p draws attention to 2p and 8p. That is a shape relationship, not yet a safety conclusion.
What does the inference remove?
The block 23m waits on 1m and 4m. If the rules establish that an opponent cannot ron 4m, that exact two-sided wait is unavailable, removing one common route by which 1m could deal in.
One route is not every route. The opponent could still wait on 1m as:
- A single pair wait
- One half of a double-pair wait
- A completion in a special form
- A new wait after changing the hand
- A legal discard win in rules without furiten
Suji lowers selected two-sided risk; it does not make risk zero.
One side and both sides
The central tile 4m belongs to both the 1–4 and 4–7 relationships.
- If only the condition around 1m is available, only the 23m route waiting on 4m is removed.
- If both 1m and 7m conditions apply, the 23m and 56m two-sided routes to 4m are both removed.
Even then, 4m can complete an inside 35m, a pair in a double-pair wait, or a single wait. Removing both two-sided routes is not absolute safety.
Why does suji fail?
- Inside wait: 35m waits only on 4m.
- Edge wait: 12m waits on 3m and does not follow the full two-sided inference.
- Double-pair wait: 44m plus another pair can wait on 4m.
- Single wait: a lone 4m can need another 4m for the head.
- Wait change: an early discard describes an earlier hand, not necessarily the current one.
Why do rulesets produce different conclusions?
The number geometry transfers. The legal meaning of an opponent’s prior discard does not.
Japanese Riichi
Furiten restricts discard wins, and a riichi hand is generally fixed. A specific riichi player’s discard row therefore provides strong rules-based information. Suji still removes only two-sided paths and remains weaker than genbutsu.
Taiwanese and Cantonese Mahjong
Most tables do not use the same furiten system. An opponent who discarded 4m can later change to a wait involving 4m or its related tiles and may still win under the table rules. Suji is then a shape and behavior clue, not a protected safe tile.
Suji belongs to one opponent
If player A discarded 1m and player B discarded 7m, those do not form both sides against player A. Each concealed hand and wait is independent.
Against multiple possible tenpai players, maintain separate sets of:
- Discards
- Open groups
- Likely suits
- Visible structures
- Rules restrictions
A tile relatively safe against A may remain dangerous against B.
A defensive workflow
- Identify whether the rules include furiten or another discard-win restriction.
- For one opponent, find tiles protected directly by the rules.
- Use suji only to remove selected two-sided routes.
- Add kabe, visible tiles, calls, and likely patterns.
- Preserve the exceptions: inside, double-pair, single, and changed waits.
- Combine the result with your shanten, value, and draws remaining.
Common misunderstandings
- Three-apart means safe.
- Both sides eliminate every possible wait.
- Different players’ discard rows can be merged.
- Riichi furiten can be imported into Taiwanese or Cantonese rules.
- Suji has one universal safety percentage.
Risk changes with rules, turn, visible tiles, hand type, and opponent. A context-free percentage is not supportable without a defined dataset.
Scope and limitations
This article explains which shapes suji can remove. It does not assign a fixed deal-in rate. Formal play follows the current rules, and any statistical claim requires a defined ruleset and reproducible game sample.
Separating efficiency from defense in Tingpai Lab
Tingpai Lab primarily compares hand structure and near-term self-draw routes. Suji belongs to opponent information and defense, so it cannot be derived from pure efficiency alone. Find the offensive candidate first, then decide whether table pressure requires a defensive correction.
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